1. Field of the Invention
The present invention is directed to an axial seal device and to an improvement in a rotary drill using an axial seal device and more particularly to an automatic wear compensating axial seal apparatus which uses a Belleville spring to bias two sealing members together. The biasing force of the Belleville spring is applied to one of the sealing members such that it is held in contact with the other sealing member and as wear occurs, on the contact faces of the sealing members, the Belleville spring exerts a force which continues to maintain contact between these surfaces. Furthermore, the present invention is more particularly directed to a rotary drill bit which incorporates the improvement of this type of an automatic wear compensating seal apparatus.
2. Description of the Prior Art
In prior art devices where it is necessary to provide a seal between two elements which move relative to one another, the most common types of seals are annular seals such as those shown in U.S. Pat. No. 4,154,312, which is directed to a Barnetche bit which is a rotary drill bit having a solid conical cutting head. The annular seals used in this reference are typical in that the annular sealing members are placed in grooves formed in one of the two members which are being sealed. The diameter of the annular sealing member is selected to be equal to the diameter of the groove so that the annular sealing member is not under any elastic force. The seal is formed by the peripheral surface of the annular sealing member which contacts the first member in the groove and the second member on the surface thereof. As a result of wear, the cross-sectional diameter of the seal will decrease and eventually the peripheral surface of the seal will not contact both the surface of the groove and the surface of the other element. At this point, the seal will lose its sealing effect.
Once the seal has lost its sealing effect and harmful elements in the environment in which the sealed device is operating can enter the interior of the device causing damage to other parts of the device. In a device such as the rotary drill bit shown in U.S. Pat. No. 4,154,312, that portion of the drill bit which wears first is the seals. In order to replace the seals, it is necessary to withdraw the drill bit from the bore hole, remove the cutting head, add new seals, replace the cutting head and then place the drill bit down the bore hole again. This is a time consuming task and, therefore, the change of seals is a costly operation as a result of the lost time. Furthermore, failure to change the seals can cause serious damage to the internal elements of the drill bit.
Another type of prior art seal is a helical spring or bellows seal. This type of seal provides wear compensation since the sealing surfaces are perpendicular to the axis of the helical spring or bellows and the helical spring or bellows are compressed in order to bias the seal surfaces together. Although this type of seal provides compensation for wear, the sealing devices are complicated and costly and furthermore, have several disadvantages. First, they require a large amount of longitudinal space. The longitudinal space occupied by the seal is significant because the nozzle of the drill bit should be as low as possible. Further, the bellows are constructed of a thin metal convolution which cannot withstand the agressive environment found in drilling.
Still another type of seal found in drill bits is one in which an elastic annular member is positioned between a drill bit and cutting head with the annular member forming a seal against an inclined plane. This type of seal is shown in U.S. Pat. No. 3,299,973. Seals of this type will not, however, withstand the extreme conditions often found downhole in the drilling of wells and the seal will be subject to leakage under the extreme pressures and to damage caused by the rotation of the cutting head with respect to the drill bit and the destructive materials found in a downhole environment.